The invention relates to an accident sensor for detecting an impact.
The accident sensors currently used are designed as so-called acceleration sensors. In the event of an accident, they detect the acceleration or deceleration that occurs upon impact. If the acceleration or deceleration exceeds a critical value, motor-vehicle safety devices, such as seat-belt tighteners or airbags, are triggered. Usually, a plurality of acceleration sensors is mounted to the motor vehicle, with each acceleration sensor detecting the acceleration or deceleration in one spatial direction for detecting a front or side impact, as well as rolling of the vehicle.
A disadvantage of these sensors is that an acceleration sensor is required for each spatial direction. Also, such sensors cannot determine the site of the impact. These systems do not directly determine the impact and the associated deformation of the motor vehicle, but only the acceleration or deceleration resulting from the deformation.
U.S. Pat. No. 4,346,914 discloses an impact-detection device that responds to acoustical oscillations in the bearing parts of the vehicle body. The acoustical signals are converted into electrical signals by one or more piezoelectric force sensors that is or are connected to one or more acoustical waveguides. The latter comprise thin steel tubes that extend from the central installation point of the sensor(s) into the regions of the body that are at risk for impact, and serve there in the acoustical coupling with bearing parts that are spot-welded at numerous locations. The signals are processed by a microprocessor. The signal processing constitutes the basis of the determination of an impact situation that would require the triggering of the passenger-restraint system.
A disadvantage of this system is that the sound waves are contained in a complicated tubular waveguide system, and transported from there to a central piezo-element that converts the sound waves into a voltage signal. This voltage signal is then conducted further to a microprocessor. Not only is the processing of the tubular system complex and costly, but it is not possible to ascertain the origin of the signal with this apparatus. It only recognizes the severity of the accident. The sensor cannot identify the site of the deformation.
DE 37 29 019 A1 describes a device for triggering a safety apparatus. In this case, due to the association of sound and/or structure-borne-sound sensors, a system is shifted in position for differentiating an impact against an obstacle from other, corresponding noises and disturbances under critical driving conditions.